The present invention relates to field emission display backplates and methods of forming field emission display backplates.
Field emission displays are utilized in a growing number of applications. Some conventional field emission display configurations include a cathode plate, also referred to as a backplate, having a series of emitter tips fabricated thereon. The emitters are configured to selectively emit electrons toward an opposing screen of a faceplate to produce an image. Such a screen is typically coated with a phosphor to produce an image responsive to emitted electrons striking the screen.
Multiple emitters are typically utilized to excite a single pixel. For example, hundreds of emitters may be utilized for a single pixel. Individual pixels can contain a deposited one of red, green or blue phosphor.
A grid, also commonly referred to as a gate, comprising a conductive material such as metal or polysilicon is preferably formed adjacent and spaced from the emitter tips. The gate is preferably positively charged providing an anode to selectively control the emission of electrons from a corresponding emitter. Inasmuch as the substrate is usually grounded or provided at a lower voltage potential, the selective application of a positive voltage to the gate results in the selective emission of electrons from the corresponding emitter. Further, the corresponding screen of the faceplate may be positively charged to attract emitted electrons. An exemplary field emission display configuration is described in U.S. Pat. No. 5,229,331, assigned to the assignee of the present invention, and incorporated herein by reference.
It has been observed during operation of conventional field emission displays that undesired or spurious electron emission from the emitter to the grid or gate electrode can occur. Such emitted electrons proceed in a substantially horizontal path and are drawn to the gate electrode as opposed to being drawn to the phosphor screen of the faceplate as desired.
Referring to FIG. 1a-FIG. 1c, a process for fabricating an emitter and grid construction of a conventional field emission display backplate fragment 10 is illustrated. Referring specifically to FIG. 1a, fragment 10 includes a bulk substrate 12. Substrate 12 comprises a monocrystalline silicon wafer, or polysilicon or amorphous silicon on a glass substrate. A layer of first material 13 and a layer of second material 14 are formed within bulk substrate 12. The first and second layers can be doped with impurities to provide pxe2x88x92 semiconductive material 13 and n+ semiconductive material 14, respectively. A mask 9 is formed over substrate 12.
Referring to FIG. 1b, isotropic and/or anisotropic etching of the structure of FIG. 1a provides an emitter 11 which extends from a surface of substrate 12. The etch is timed such that emitter 11 typically comprises substantially n+ semiconductive material 14.
Referring to FIG. 1c, a conformal layer of insulative material 18 is deposited over substrate material 13 and emitter 11 following the formation of emitter 11. Thereafter, conductive material 16 having surfaces 17 is formed over the layer of insulative material 18. Field emission display backplate fragment 10 may next undergo chemical-mechanical polishing to remove portions of the conductive material and the conformal insulating material which extends beyond emitter 11 as described in U.S. Pat. No. 5,229,331. The chemical-mechanical polishing step exposes the insulative layer about emitter 11. Wet etching of the insulative layer forms the depicted regions of insulative material 18 and exposes emitter 11.
An electrical field is generated intermediate surfaces 17 of grid 16 and emitter 11 to provide electron emission from emitter 11 through an opening 15 within grid 16. During operation, spurious electrons may be drawn in a substantially horizontal direction towards grid 16 as opposed to a direction through opening 15. Such is undesired. This problem is particularly acute in applications where the spacing intermediate grid surfaces 17 and emitter 11 is reduced to provide a field emission display backplate structure 10 which is operable with lower turn-on voltages.
Referring to FIG. 2, a conventional structure utilized to reduce the emission of spurious electrons from emitter 11 to grid 16a is illustrated. More specifically, increasing the spacing intermediate the outer surface of emitter 11 and surfaces 17 of grid 16 reduces the flow of such spurious electrons to grid 16.
Conventional field emission display fragment 10a can be formed utilizing a reflow processing step. More specifically, following the formation of the conformal insulative layer, a reflow process step is conducted to reduce the slope of portions of the insulative layer over emitter 11. Thereafter, a conductive layer is deposited over the reflowed insulative layer to form grid 16a. Such provides surfaces 17a of grid 16a having reduced slopes compared with grid surfaces 17 shown in FIG. 1c and represented as dashed lines. In particular, the depicted grid 16a includes surfaces 17a which are pulled back from emitter 11 compared with surfaces 17 of grid 16 of FIG. 1c. Fragment 10a of FIG. 2 provides reduced spurious electron emission from tip 11 to grid 16a compared with the emission of spurious electrons from tip 11 to grid 16 of FIG. 1c. 
However, the described reflow processing technique of the conformal insulative layer has some disadvantages with respect to field emission display backplate processing. For example, the reflow temperature of the insulative material may exceed the strain point of some glass substrates resulting in damage to the structure. Further, the reflowed insulative layer may have a non-uniform thickness across the substrate because of possible varied temperatures across the substrate during the reflow processing step. Also, reflow processing techniques are often difficult to implement in arrangements having a large number of tips in close proximity to one another because of increased surface tension. Numerous tips are typically provided within field emission display backplates to reduce non-uniform characteristics of individual ones of the tips. In addition, opening 15 formed within grid 16a is sensitive to chemical-mechanical polishing inasmuch as grid 16a has been pulled back from tips 11.
Therefore, there exists a need to provide improved field emission display backplate structures and processing methodologies of the same which overcome the problems associated with the prior art.
The present invention includes field emission display backplates and methods of forming field emission display backplates. According to a first aspect, a field emission display backplate includes a substrate having a surface and an emitter which extends from the surface of the substrate. Further, an anode having an upper surface, a lower surface, and an opening surface, is formed spaced from the emitter. The opening surface defines an opening aligned with the emitter and the opening surface includes a first portion which curves outward relative to the anode and a second portion which curves inward relative to the anode.
According to some aspects, the emitter has a surface including an inner surface portion which curves outward relative to the emitter and an outer surface portion which curves inward relative to the emitter. The outer surface of the emitter can be parallel to the opening surface of the anode. The emitter has a length in a direction substantially orthogonal to the surface of the substrate. The inner portion of the emitter has a length comprising approximately 15 percent to 95 percent of the length of the emitter according to some aspects.
The present invention includes other aspects wherein the emitter includes an inner portion comprising a first doping type semiconductive material and an outer portion comprising a second doping type semiconductive material. For example, the inner portion of the emitter can comprise p-type semiconductive material and the outer portion can comprise n-type semiconductive material.
The present invention also includes methodologies for forming field emission display backplates.